Files are also often moved between file servers in order to relocate infrequently accessed files from feature-rich, expensive, and highly-protected high-speed disk storage to more economical and possibly slower mass storage. In such a hierarchical storage system, the high-speed disk storage is referred to as primary storage, and the mass storage is referred to as secondary storage. When a file is moved from a primary file server to a secondary file server, the file in the primary file server is typically replaced with a corresponding stub file that contains attributes of the file including a link to the new file location in the secondary file server. The stub file can be accessed to redirect an access request from a client to the new file location in the secondary server, or to migrate data from the file location in the secondary server back to the primary file server. The migration can be performed in accordance with a selected service level policy, for example, as described in “Information Lifecycle Management: an Automated Approach,” Technical White Paper, EMC Corporation, Hopkinton, Mass., Dec. 8, 2003.
For applications that must comply with certain regulatory requirements, a file server may ensure content authenticity and retention of data for a certain period of time. Such regulatory requirements include Securities Exchange Commission (SEC) Rule 17a-4, stock exchange (NASD/NYSE) supervision requirements, and the Sarbanes-Oxley Act. For example, data have been written to CD-R optical disks to ensure content authenticity and retention of the data.
More recently, a file server using a redundant array of inexpensive magnetic disks (RAID) has been configured for ensuring content and ensuring Write Once Read Many (WORM) semantics. For example, a Centera (Trademark) brand of magnetic disk-based WORM device has been offered by EMC Corporation in connection with a policy engine for automatically moving reference data from primary storage to the WORM device. As described in “EMC-LEGATO E-mail Archiving Solution,” Solution Sheet, EMC Corporation, Hopkinton, Mass., July 2004, the Centera (Trademark) brand of magnetic disk-based WORM device has been used for retaining e-mail for a set period of time and also making the e-mail instantly accessible.
Another method of file retention protection is known as file level retention (FLR). Typically FLR uses a volume or file system attribute for indicating retention period protection in connection with file attributes such as a “read-only” flag and the “last accessed” attribute. If the volume or file system attribute is set, then the setting of the “read-only” flag for a file in the protected volume or file system gives the file and its pathname WORM properties. Once the “last accessed” attribute for such a protected file is set with a retention date, the file cannot be altered or deleted until after the retention date. See, for example, Henry Baltazar, “SnapLock Locks Down Info,” eWeek.com, Woburn, Mass., Oct. 30, 2003.